GEAR OIL LEAK

[stirlinggaz]

Hi all,
what started off as a few small spots of oil, has turned into a rather big patch of oil!
its definately gear oil. (recognise the smell, lol)
thing is, knowing how oil leaks are (ie usually turns out to be the furthest away place from where you originally thought it was, lol)
what would be the usual suspects?
it isnt the clutch cover gasket. (pretty sure of that, seeing as i used a load of instant gasket on it, lol)
so im thinking its either the seal behind the front sprocket or the one on the selector shaft.
pretty convinced its likely to be the one behind the sprocket.
do these just pull out (with self tappers) & is it easy to fit new ones?
do they have a lip on them?
im presuming i'd need to tap it in with a drift or hollow tube?
any advice, before i butcher it?
cheers,
GAZ